1. Field of the Invention
The present invention relates to composite articles of manufacture comprising metallic members attached to a relatively fragile non-metallic member by magnetic pulse forming and methods of fabrication thereof, and more particularly, the present invention relates to high voltage fuse construction involving the attachment of a metal ferrule to a relatively fragile cylindrical housing by magnetic pulse forming and methods of fabricating thereof.
2. Description of the Prior Art
Magnetic pulse forming machines were first introduced in 1962. Since that time, magnetic pulse forming machines have been utilized to assemble a variety of composite articles of manufacture which would be difficult and costly to assemble by conventional methods.
Magnetic pulse forming is an assembly technique which utilizes a high intensity magnetic field to expand or contract metallic work pieces. Magnetic pulse forming is based on the interaction of a rapidly changing magnetic field and the currents induced in an electrically conductive work piece. Magnetic pulse forming is capable of compressing or expanding metal members without direct physical contact and without lubricants or torque normally encountered in rolling and spinning operations.
The high flux densities necessary to perform such magnetic pulse forming can be produced in the absence of a material of high permeability by discharging a capacitor through a coil for a period of a few microseconds. Thus, tremendous flux densities are produced for a short period of time. Further, since it is the magnetic force which moves the metal, the introduction of a non-cnductive material between the work piece and the magnetic field producing member has no effect on the assembly operation, although more energy is required for this type of operation because of the increased distance through which the magnetic field must act.
Magnetic pulse forming is particularly advantageous to form metallic members to non-metallic members. For example, brass tubing and aluminum sleeves may be successfully assembled to Bakelite and/or phenolic materials to provide structurally sound joints. The time consuming and costly spinning operations generally required for such assemblies are eliminated when the parts are assembled magnetically.
However, some difficulty is experienced when assembling metallic members to non-metallic relatively fragile members. For example, many non-metallic materials have a relatively high tensile strength but a relatively low compressive strength. Consequently, extreme care must be utilized when compressing such metallic members onto such non-metallic members by magnetic pulse forming to prevent fracture of the non-metallic member. A further problem is experienced where the metallic members must be of sufficient strength to withstand stress forces applied to the metallic member but the member must be compressed onto a relatively fragile non-metallic member. Since the metallic member must be thick enough to withstand the stress applied, a relatively large magnetic force must be applied to compress the metallic member onto the non-metallic member by magnetic pulse forming. Often in such circumstances, magnetic pulse forming is not suitable since sufficient force cannot be applied to compress the metallic member without also fracturing the non-metallic member.
Accordingly, it would be a desirable advance in the art to provide a composite article of manufacture including a relatively fragile non-metallic member upon which is attached a metallic member by magnetic pulse forming and methods of fabrication thereof which avoid the above mentioned problems.